First of all, I think that you have your knot "reference" somewhat different than mine.
I mean, in 30 knots with gusts to 35, I'm probably on a 4.0 + 83L max.

But anyway, in rough conditions, the smaller the board the easier it gets.
For instance, when I haven't got the balls anymore to use my IS101 (ex IS97) with my 6.7, I just change the board for my IS87 and it becomes much easier and controllable again, with the same 6.7 sail.